As Boston continues in a state of emergency, with police having shot one suspect dead and in pursuit of a second suspect believed to be responsible for Monday's marathon bombings, authorities are tightening security in preparation for two major runs in Europe.

The London Marathon, one of the world's biggest road races, and the Hamburg Marathon, a high-profile run in the northern German city, both kick off Sunday. Local – and the world's – media are expected to tune in, hoping against a repeat of the U.S. attacks.

Security in London was put on high alert after the Boston bombings, which occurred as that city's marathon was drawing to a close. The attacks left three dead and more than 170 badly injured. Fears of a coordinated or copycat attacks has the U.K. bracing itself ahead of Sunday's run. Deputy Prime Minister Nick Clegg said the authorities have spent the week "double, triple, quadruple checking" security arrangements for the event.

Scotland Yard said Friday it had added several hundred more officers, increasing their presence by some 40 percent compared with last year's marathon, to guard the runners and spectators planning to attend.

The London Marathon, first run in 1981, is expected to have a field of 36,000 runners. One of the world's biggest marathons, the run will be the first international race of its kind following Monday's blasts in Boston.

At the start line, runners will be asked to pause for a 30-second silence in memory of those killed in the American attacks. Organizers will also hand out black armbands for contestants wanting to commemorate the dead.

The race's route winds round landmarks like Tower Bridge and goes through the Canary Wharf financial district before ending in front of Buckingham Palace.

U.K. government home secretary Theresa May confirmed security would be stepped up along the 26-mile (42-kilometer) run.

"They have made some adjustments to the policing arrangements for the marathon and they have put some increased policing in," May told a committee of legislators, according to reports.

A host of celebrity runners including Welsh opera singer Katherine Jenkins, ITV news' Royal correspondent Tim Ewart and actress Juliet Oldfield are scheduled to run in the charity fundraiser in London. British Olympic gold medalist Mo Farah is also scheduled to take part, though he will only run the first half of the marathon.

It will be Britain's second big security test in the space of a few days after Wednesday's ceremonial funeral for former Prime Minister Margaret Thatcher,which passed without incident.

Across the continent in Hamburg, plans to stage its annual race will also go ahead as planned.

Jorg Ziercke, head of the BKK, the German equivalent of the FBI, warned of "panic mongering" following the bomb attacks in Boston. While Ziercke said there can “never be 100 percent security,” he added that Hamburg's police have learned from the situation in Boston and adjusted their security measures. He did not go into detail except to say there would be a very visible security presence at the marathon, which he said would have a "preventive and deterrent” effect. Ziercke added that authorities have no concrete evidence of any planned attacks in Germany.

Some 15,000 runners and crowds of more than 750,000 are expected to take part in the Hamburg marathon, whose 26-mile course winds its way through the city, from the Reeperbahn red light district past Hamburg's legendary harbor and through some of its most exclusive quarters. A number of local celebrities, including German talk show host Johannes B. Kerner and several local soccer stars, have signed up for the run.

Hamburg marathon organizer Frank Thaleiser said that far from scaring people off, the attacks in Boston seemed to have strengthened the resolve of local runners to show solidarity with the American city by taking part. Speaking to German tabloid Das Bild, Thaleiser said the reaction of “99 percent” of registered runners was “now more than ever!”